DESCRIPTION The etiology of schizophrenia, a common devastating mental illness, is unknown. There is a significant genetic predisposition for schizophrenia, therefore, identification of genes predisposing to this disease would aid in the identification of at-risk individuals, and may lead to a rational, versus empirical, method of treatment. Using case-control studies, variation at two loci (HLA DQB1 and the dopamine D3 receptor, DRD3), have been associated previously with susceptibility to schizophrenia. In collaboration with researchers in New Delhi, the investigators will test the hypothesis that these two loci affect susceptibility to schizophrenia. First, they will recruit 100 Indian families having two or more siblings with schizophrenia, then they will genotype DNA samples from these family members for polymorphisms at the two loci, and finally, they will perform statistical genetic analyses.